The DnaB protein is the primary replicative helicase in E. coli and its active form is a hexamer ring. It was reported that this ring has a strong 3-fold symmetry, suggesting that it was a trimer of dimers. We have found that under different conditions, using a variety of nucleotide cofactors, we always find two different forms of the DnaB ring, one with 3-fold symmetry and one with 6-fold symmetry. Mass analysis using the STEM showed that both forms were indeed hexamers, ruling out the possibility that the 3-fold form was actually a trimer. We have also found rings that are in an intermediate state between these two forms. This suggests that there may be two different conformations of the hexameric ring, with cooperative transitions between the two states.